A person working at cold temperatures (for example 40° F. or less) under winter conditions or staying outdoors under very cold conditions, e.g., in arctic areas, has to breathe in great amounts of cold, dry air. This is not only unhealthy, but also substantially increases the loss of heat of the person as the body tends to warm up the inhalation air to the temperature of the body, and this amount of heat is removed from the body with the exhalation air. In addition, dry inhalation air has a disadvantageous effect on the normal moistness of the mucous membranes of the respiratory passages.
The detrimental effects of breathing cold air, particularly for people with medical problems such as cardiac conditions, angina, and asthma, and the benefits of heating inhaled air, have been recognized for many decades. Respiratory heat exchangers are intended to transfer heat, water vapor, or both between incoming and outgoing ventilation airstreams so as to keep the user warm. Through natural breathing of the wearer, the airstream is alternately directed through the entire exchange device first in one direction and then in the opposite direction.
Known heat transfer devices have been described as falling into one of three categories: (1) those designed primarily for the exchange of sensible heat; (2) those designed primarily for the exchange of latent heat; and (3) those designed to exchange both sensible and latent heat (the so-called “enthalpy exchangers”). To maximize the benefit of respiratory heat exchangers, it is desirable to choose a heat exchange material that is capable of providing high sensible and latent heat exchange efficiencies. Devices that heat and humidify inhaled air with exhaled air by passing the air though an exchanger fabricated from either foil, a nonwoven resilient porous fibrous organic polymeric material, a foraminous heat conductive material, or a continuous strip of wire netting wound helically are known. Other such devices provide a strip of thermally insulative material retained within a bandanna and positioned adjacent the mouth of a user. The use of metal, wool, uncoated metal strips, certain coated Kraft papers, and other fibrous cellulose materials tend to be unsatisfactory because the latent heat exchange efficiency of these materials is relatively poor, as compared to the sensible heat exchange efficiency. Inhaled air has been heated with electrical heating elements and with heated water. Inhaled air has also been heated by devices that obtain heat from portions of the human body rather than external power sources.
Widespread use of a device for warming air that is breathed in requires that the device be relatively small, lightweight, and inexpensive. Currently, there is widespread use of devices that cover the face in cold weather. Some such devices incorporate a heat exchange respiratory device. Available devices, however, are either unwieldy, very heavy, very expensive to manufacture, or not durable. In addition, none provide for the most efficient use of a heat-exchanging medium. Therefore, it can be appreciated that there exists a continuing need for a new and improved heat exchanger that can be used for maintaining warmth in a wearer. In this regard, the present invention substantially fulfills this need.